Question

I presume this isn’t a common problem, which makes it a bit more difficult to answer. Any help is appreciated though.

I need to call this delegate a number of times in my app, and i noticed that after a number of times, the delegate starts to come back as NULL (and hence stops responding). I put an nslog everywhere the delegate gets called, so i know that at this point, it’s fine:

UIImage *image = [self.delegate largeThumnailForMediaAtIndex:indexPath.row];

Then the next time this line gets called, the delegate is set to NULL. No lines around it call or set the delegate. I put an NSLog on the setDelegate method too, and that didn’t get called before it changed to NULL.

Any code you might need to see, let me know. Any ideas you want me to try out, let me know about that too.

Thanks for your help.

EDIT: Bizarre, but might help to lead to a solution. I put an NSTimer scheduledTimer.. in the class which gets made the delegate, and got it to fire that once a second so I could see if it turned null at any point. The result i got, however, was that this time it didn’t turn null. It returned all of the delegate methods. When i took the timer out, it goes back to returning NULL. Obviously having a timer in there is an odd workaround ‘solution’. I’m hoping this rings a bell for someone and gives them a clue to where the problem might lie?

EDIT 2: I’ve solved this problem by, instead of using this code in my AppDelegate:

JCreateViewController *create = [[JCreateViewController alloc] init];
    [create.navigationBar addLeftButtonWithTitle:@"Back" type:JButtonTypeArrow];
   create.navigationBar.title = @"Entry #17";
    [self.window addSubview:create.view];

Declaring it in my header file, then using this:

self.create = [[JCreateViewController alloc] init];
    [self.create.navigationBar addLeftButtonWithTitle:@"Back" type:JButtonTypeArrow];
    self.create.navigationBar.title = @"Entry #17";
    [self.window addSubview:self.create.view];

I don’t understand why this makes a difference though. I’d love to know, if anybody does know?

Answer 1

Looks like you’re using ARC. Whatever this object is, nothing owns it. Nothing has a strong reference to it, so it gets released, and then at some point it gets deallocated.

JCreateViewController *create = [[JCreateViewController alloc] init];

This is a local variable. When the variable goes out of scope at the end of the method, you can’t access that object anymore. Under MRR, this would be a leak. Under ARC, the object is going to die, just like it was in an autorelease pool.

self.create = [[JCreateViewController alloc] init];

By creating a property (presumably strong) and putting the controller into that property, you’ve given whatever self is an owning reference to the controller. It will now live as long as the property isn’t reassigned or set to nil.

The timer fixed things because the timer retains its target (which I believe was the controller (your question is rather unclear)), and the timer itself is retained by the run loop. So the run loop keeps the repeating timer alive and the timer kept your controller alive.

In short, make sure something owns this object and it’ll stick around.